Heretofore, color television picture display devices have mainly used cathode-ray tubes. Cathode-ray tubes have excessively large depth in comparison with their screen face sizes. Hence it has been impossible to make a flat type television receiver using a cathode-ray tube. To overcome this problem, developments of display devices of various types as for the flat-type display device, such as an EL (electroluminescence) display device, plasma display device, and liquid crystal display device, have been developed. None of them can offer satisfactory performance in brightness, contrast, or color reproducibility. Then, aiming at obtaining displays of color television pictures on a flat-type device by employing electron beams which is capable of producing as high quality pictures as an ordinary cathode-ray tube can offer, there have already been picture display devices wherein a picture on its screen was divided into an array of segments of matrix arrangement without leaving blank spaces therebetween and a fluorescent screen of each segment was lit by each electron beam belonging thereto which was deflected and scanned by an adequate means, thereby as a whole, a color television picture was constructed. In the following, referring to the drawings, the above-mentioned picture display device of prior art is elucidated.
FIG. 1 shows an internal constitution of a picture display device of this prior art. In FIG. 1, numeral 101 is a back electrode, numeral 102 represents--therefor linear cathodes as electron beam sources, numeral 103 is an electron beam extraction electrode, numeral 104 are signal electrodes, numerals 105 and 106 are focusing electrodes, numeral 107 is a horizontal deflection electrode, and numeral 108 is a vertical deflection electrode. These elements are stored in glass envelopes 109 and 110 and the inside of the envelopes are evacuated. The linear cathodes 102 are spanned in the horizontal direction so that they produce electron beams having horizontally uniform distribution, and a plural number of such linear cathodes 102 (here, only four of 102a to 102d are shown) are provided with an adequate spacing. These linear cathodes 102 are constituted by, for example, coating an oxide cathode material on the surface of tungsten wires. The back electrode 101 is composed of a planar conductive material, which is disposed in parallel with the linear cathodes 102a to 102d. The extraction electrode 103 counterfaces to the back electrode 101 having linear cathodes 102a to 102d therebetween, and it is composed of a conducting plate having arrays of through-holes 111 provided in the horizontal direction with an adequate spacing over horizontal lines counterfacing to respective linear cathodes.
Although these through-holes 111 are of circular shape in the present working example, it may be such shapes as oval or rectangular, or slit. The signal electrodes 104 are composed of conducting plates 112 which are oblong in the vertical direction and disposed at positions respectively counterfacing to the through-holes on the extraction electrode 103 with having a required distance, and on respective extraction electrodes, at the positions counterfacing to the through-holes 111 of the extraction electrodes 103, similar through-holes 113 are present. The shape of the through-holes 113 may be oval or rectangular shape, or also slit which is oblong in the vertical direction may be used. The focusing electrodes 105 is composed of a conducting plate having through-holes 114 at the positions respectively counterfacing to the through-holes 113 of the signal electrodes 104. As the shape of through-holes 114, circular or oval shape, or slit may be used. The focusing electrode 106 has slit holes 116 which are extending vertically at the positions of through-holes 114 of the focusing electrode 105. As for the shape of the slit holes 115, circular, oval or rectangular shape may be used. The horizontal deflection electrode 107 is comprised of two conducting comb-shaped plates 116 and 117 which are connected at their end parts and mutually engaged with keeping an adequate spacing over a single plane, and a space 118 formed between conducting plates 116 and 117 are facing to through-slit-holes 115 of the focusing electrode 106. The vertical deflection electrode 108 is, as shown in FIG. 2, comprised of a constitution that two conducting plates 119 and 120 which are connected at their end parts, that is, a constitution that two pieces of comb-shaped conducting plate 119 and 120 are mutually engaged keeping an adequate spacing over a single plane. A screen 121 is constituted by coating, over the inner face of an envelope 109, a fluorescent material layer 122 which emits light by the illumination of electron beams and then by adding a metal-back layer (not shown in the FIGURE) thereonto. And, the above-mentioned extraction electrode 103, signal electrode 104, focusing electrodes 105 and 106, horizontal deflection electrode 107, and vertical deflection electrode 108, are jointed respectively by an insulating adhesive (here, not shown in the FIGURE), thereby an unity electrode block 124 is formed.
On a picture display device constituted as described above, its operation is elucidated below.
First, in order to make the electron emission from the linear cathode 102 easy, it is heated by flowing a heater current. Under the state of heating, the back electrode 101, by impressing adequate voltages onto the linear cathodes 102 and the extraction electrode 103, sheet-shaped electron beams are emitted from the surface of the linear cathodes 102. The sheet-shaped electron beams are then divided into a plural number of electron beams by the through-holes 111 of the extraction electrode 103 and they become a plural number of electron beam flows 123. These electron beam flows 123 are adjusted on their passing amounts for respective electron beam flows by the signal electrodes 104 corresponding to the video signal impressed on the signal electrode 104. Next, after the electron beams passing through the signal electrodes 104 are focused and formed by the electrostatic lens effect of the through-holes 114 and 115 of the focusing electrodes 105 and 106, they are deflected by the potential differences given to the adjacent conducting plates 116 and 117 of the horizontal deflection electrode 107 as well as to the adjacent conducting plates 119 and 120 of the vertical deflection electrode 108. Furthermore, a high voltage (for example, 10 kV) is applied on the metal back layer of the screen 121, and hence the electron beams are accelerated up to a high energy and collides with the metal back to make the fluorescent material 122 emit light.
When the television picture screen is divided horizontally and vertically into a matrix shape and an assembly of small segments 125 is formed, by allotting one electron beam which is separated as described above to each of those small segments, and by deflecting and scanning each electron beam only within each small segment, a whole picture can be displayed on the screen. And by controlling the RGB video signals corresponding to respective picture elements by the signal electrodes 104, television moving pictures can be reproduced.
In the constitution as has been described above, for obtaining a high quality picture images all the time, problems described below were present.
As is shown in FIG. 2, the linear cathodes 102a to 102d are thin wires of a diameter of 10 .mu.m, at their both ends (only one side is shown) their height is limited by a height limit bar 126, and their position in the Y direction is determined by a Y-direction positioning frame body 127. Furthermore, the tension is given at both sides or at one side by springs 128 which are attached to the Y-direction positioning frame body 127.
When vibration is applied to the picture display apparatus including positioned and spanned linear cathodes 102a to 102d, the linear cathodes 102a to 102d start vibration containing mainly the simple harmonic vibration as shown in FIG. 3 and keep this vibration until it is damped out. When the linear cathodes 102a to 102d vibrate, amount of electron beams 123 passing through the through-holes 111 of the above-mentioned extraction electrode 103 varies periodically (not shown), and eventually the brightness on the screen varies periodically, hindering achieving stably a high quality picture image.
Heretofore, as for the prevention means of the vibration of the linear cathodes, there has been a means using cathode electrode control lines as disclosed in a Gazette of Tokkai Sho 50-10958. In the following, explanation is given referring to the drawings.
As shown in FIG. 4 and FIG. 5, cathode control lines 2 are spanned perpendicularly with respect to the spanning direction of linear cathodes 1, and they are held so as to keep a constant distance from the above-mentioned linear cathodes 1. Then, if a certain external force is applied to the structural body, although the above-mentioned linear cathodes start the vibration containing mainly the simple harmonic vibration, when they touch the cathode control line 2, the amplitude is controlled and damped, and thereby the vibration is suppressed. And, the above-mentioned cathode control wires 2 are disposed with predetermined intervals, not with a constant interval, and thereby, as shown in FIG. 4, the resonant vibration due to the second-order vibration of the above-mentioned linear cathode 1 having its nodes at the above-mentioned cathode control lines 2 can be prevented.
Hereupon, in FIG. 4, numeral 3 is an electrode, numeral 4 is a height limit bar for the linear cathodes 1, numeral 5 is a Y-direction positioning frame body for the linear cathodes 1, and numeral 6 are spring elements for spanning the linear cathodes 1 by giving tension thereon.
In the constitution as has been described above, in order to obtain a high quality picture images all the time, there have been problems to be described below.
In a picture display device for the display use, in case that cathode control lines are disposed in the working picture area, the electric field is disturbed and uniform electron beams cannot be produced and hence a uniform picture image cannot be obtained.
And, in case that a plural number of linear cathodes are used, it is very difficult to keep the distances between the above-mentioned cathode control lines 2 and the above-mentioned linear cathodes 1 uniform for respective linear cathodes, and hence the non-uniformity of the above-mentioned distances gives a scatter or dispersion on the above-mentioned vibration prevention function on the linear cathodes 1, causing a variation of the brightness on the screen; and hence a uniform high quality picture image cannot be obtained.